void LoadDS()
        {
            List <PhieuNhapDTO> dsPN = PhieuNhapBUS.GetDSPN();

            dgvDSPN.DataSource = dsPN;

            for (int i = 0; i < dgvDSPN.Rows.Count; i++)
            {
                dgvDSPN.Rows[i].Cells[0].Value = i + 1;
            }
            btnThem.Enabled = true;
            btnSua.Enabled  = true;

            txtMaNhap.Enabled = true;
            btnLuu.Enabled    = false;
        }